Endless track mechanism



` N0v-1.1e`,194s. LA KAMLOOKHINE 2,453,750

"ENDLESS TRACK MECHANISM Filed May l, 1944 2 Sheets-Sheet l NV 16, 1948 l. A. KAMLOOKHINE ENDLESS TRACK MECHANISM 2 Sheets-Sheet 2l Filed May 1, .1944v Patented Nov. 16, 1948 iJlTiED S.'lTATl:lS PATENT OFFICE 2,453,750 ENpLEssiTRACK MECHANISM Igor A.Kamlookhne, Milwaukee, .Wis., assignor to AllisrChalmers Manufacturing Company, Milwaukee, Wis., a corporation of Delaware Application May 1, 1944, Serial No. 533,485

12 Claims. lV

The invention relates toself-'laying track vehicles, and itis concernedlrnore particularly with improvements inthe construction and'operation of the track-laying'mechanisms for such vehicles.

In .self-laying track mechanismsof thev type in which an endless track belt islmounted-for travel around a supporting frame by means yof track supporting iront and re'ar wheels, itl has heretofore been Ausual to mount one of said'wheels reciprocably on the supporting frame for movement relative thereto in track! Itensioning and track releasing directions,v and to interpuso-a resilient backing unit between the frame andthe reciprocable wheel, the principal purpose of 'said arrangement being to protect the mechanism against damage when a stone or other sold'obstruction becomes lodged 'on the tra-ck 'belt-and "is forced to travel with the belt around the supporting frame, as is well known in 'the' art.

Generally, it is an object of the invention to provide an improved self-laying trackmechanism of the hereinabove mentioned character.

More specically. itisan `object-of the invention to provide an improvedself-laying track -mechanismwhich lends 'itself to use inv'ehicles which are to be driven at relatively high speedssuch as thirty or forty miles per hour;

A further objectief the invention is to provide an improved self-layingtrack mechanism'adapted for high speedV operation,` as set forth hereinbefore. and in which the track belt Willrun smoothly, that is, without'undue flopping'or whipping, when it is driven atrelatively high circumferential speeds relative to. its supporting structure.

A further object of -:the invention is .to provide improved self-laying track mechanism .which will be protected against damage in caseY a lstone or other solid obstruction becomesA lodged on the track belt. as has been stated-hereinbefore, and

whose ability to afford said protection will not be i" readily impaired by 'such causes as the formation 3d modi-ce, or rust.

, ber object of the lnventionis' .to provide an improved self-laying track mechanism'of the i ongation of the track belt andwear oi the eels cooperating with the track belt will be auticaliyv compensated tothe extent of making lent readiustments of the mechanism unnecessary.

A iur-ther obje-ct of the invention is to `provide an improve-:l: mechanism :for controllingthe tension of an endless trackbelaiand more-particularly provide;` such a' i mechanism which will satisfactorilyf'taketcarev ofth'ernrcquirements for .r1 forth hereinb'eforein which wear properly tensioning Vatrack belt of the continuously flexible type, as for instance the well-known type of 4rubber track belt'in which a continuous-A ly flexible belt member is formed by a series of rubber Vembedded steel cables.

The foregoing and other objects :and advan-,` tages'of the invention will become more fully ap-f parent'from the following description of` a preferred embodiment ofthe invention shown in the accompanying drawings. Referring 'to the'draw'- ings, in whi-ch like reference charactersdesignate` the'sa-ine or similar-parts in :the Various views:

Fig-ll is a side View of anendless track mecha` anism;

Fig; 2,'i-s an enlarged side View, partly in section, of :the track tensioning and release mechanism shown at a smaller scale in Fig. 1;

Fig. 3 is' an end View, partly in section, of-thev mechanism shown in Fig. 2;

Fig. 4 is a sectionalview on line IV-IV of lFig. 2;

. Fig.` 5,is`a detail view, partly in section, on line V".V of Fig.2 land Fig. 6 isv a sectional View, on line VI-VI of Fig. 3.

The endless track mechanism .shown'in Fig. l comprises a track frame generally designated by they reference character I', a track belt drive sprocket 2; :a track idler 3; truck rollers 4, a track supportingY roller 5, andan'endless track belt` 5 having suitable drive lugs (not shown) engages able by the drivel sprocket 2. A transmission chain for driving the sprocket wheel 2 is indicated at l, and a shaft is indicated at 8 on which the truck frame is pivoted to a vehicle body', not shown; Arranged coaxially with the shaft 8 is a driving sprocket (not shown) for the chain l, and it will: be `understoodthat power is transmitted through the chainY l. to the track belt drive sprocket 2 for purposes of propulsion. The cene ter of the sprocket 2 is retained `at axed, prete erably adjustable distance'fromthe center of sha-'ft 8', `and any suitable construction may be employed for that purpose. Likewise, the truck rollers 4 andthe track supporting Wheel E may be as-y sumed to be mounted on the truck frame in relatively xed positions, the mechanism .conforming in :this respect with well known principles of con struction and operation.

Fig. 3 shows ya section through the track belt'at the hottomof -the figure `and a corresponding section at the top of thezigure. The bottom .partof the idler-3..is.:broken away'in Fig.r 3 to show how the' lower run ofthe track belt cooperates with Ithe truck rollers 4, and the upper partpotFi'g 3 shows the relative engagement of the track belt and idler 3. It will be noted that the track for the rollers 4 is afforded by two endless rail belts S and I which are retained at the proper transverse spacing from each other by a lseries ol track shoes I I to which they are secured and which in turn are flexibly connected with cach other by the rail belts -9 and I0. The rail belts are made of rubber or rubber like material molded around a set of endless steel cables, as shown in Fig. 3 four cables I2 being shown embedded in the belt 9. and four cables I5 being shown embedded in the belt IB. Also embedded in the belt 3 are a series of cross clips I4, corresponding in number to the number of track shoes, each clip having yan ear at one side of the rail belt 3 and another ear at the opposite side of the belt for connection with the track shoe lI by means o rivets l5. The belt ID has cross clips I4 the same as the bel-t 5 for com nection with the track shoes by means of rivets I5. A guide lug IB is secured to each track shoe II inthe space between the rail belts 9 and I5 by means of the rivet-s I5 at the relatively opposed sides of the belts.

Each truck roller 4 hasa Vpair of solid rubber tires II and I8 ad-apted to roll on the rail belts 9 and I0, respectively, and each truck roller also has a pair of guide flanges I9 and 23 straddling the guide lugs I6 to limit lateral displacement of the track belt 6 relative to the truck rollers 4,

and vice versa.

The idler 3 comprises a hub sleeve 2i and relatively spaced rims 22 and 23 connected with the hub sleeve 2l by spokes 24. The rim 22 has a peripherallining 25 of rubber .or rubber like material for engagement with the rail belt 9, and the rim 23 has a .similar peripheral lining 25 for engagement with the rail belt IU. When the track belt 6 passes the idler3' the rail belts 9 and I0 bear upon the linings 25 and 26, respeci tively, and the guide lugs IB enter between the rims 22, 23,"the relatively opposed edges of the rims being suitably beveled asv shown to guide theubelt into proper engagement with the idler. An ice breaker 21 in the form of a disk is mounted between the rims 22 and 23.

" The hub sleeve-2| of the idler 3 is rotatably mounted on a tubular shaft 28 by means of ball bearings 29 and 30, the shaft 28 extending at i't-s opposite ends beyond the hub4 sleeve 2l and being internally reinforced at its opposite ends by collars 3l, as shown in Figs. 3 and 6. The shaft 28`is mounted on the truck frame I for movement in track tensioning and track releasing directions by means of two hangers 32 and 33 .one on each side of the idler 3. The hanger 32 is swingably suspended at one end or" a square tubular beam 34 of the truck frame I by means of `a pivot 35, so that the hanger can freely swing in a fore and aft direction relative to the truck frame about the axis of the pivot 35. The hanger 33 is similarly swingable about the axis of a pivot 36 mounted in alinement with the pivot 35 at the end of a square tubular beam 3l (Fig. 3) of the truck frame I'. The hangers 32 and 33 have eyes at their upper ends within the beams 34 and.31, respectively, and the pivots 35 and 53 whichextend through the eyes are nonrotatably mounted on the beams and are retained against axial displacement by heads and nuts as shown in Fig. '3. The bottom walls of the'beams 34 and 31 are cut away for some distance to permit unobstructed swinging movement of the hangers about thepivots .35 and 36 within a relatively Wdefrange'fi 1 The opposite, reinforced ends of the shaft 28 are fitted into large eyes of the hangers 32 and 33. and the shaft is secured against rotary and axial displacement relative to the hangers by set screws 33 and 39. Referring to Fig. 6, the hanger 33 has a boss 40 with a tapped hole in it to receive the set screw 39, and the tapered end of the set screw extends into a tapered hole of the reinforced end of the shaft 28. A nut on the set screw is drawn up against the boss 43 to lock it after the tapered end has been wedged tightly' into the tapered hole of the shaft. The same explanations apply to the set screw 38 shown in Fig. 2.

Resilient backing means for the idler 3 are interposed between the hanger 32 and a diagonal brace 4l of the truck frame l at one side of the idler, and said backing means are duplicated at the other side of the idler as shown in Fig, 3. Referring to Figs. 2 and 4, the diagonal brace 4I is made of square tubing, and a U-clip 42 is rigidly secured, as by welding, to the under side of the brace 4I in horizontally and vertically spaced relation to the pivot of the hanger 32. The downwardly extending legs of the Uclip have alined holes for the reception of a cap screw 43 which has a head at one side of the U-clip and a castle nut 44 at the other. A bracket comprising a pair of identical triangular plates 45 and 45 is pivotally mounted on the U-clip 42 by means of the cap screw 43, the triangular plate 45 being received between the castle nut 44 and one leg of the U-clip, and the plate 46 being received between the head of the cap screw 43 and the other leg of the U-clip. The castle nut is adjusted on the screw 43 and retained by a cotter pin 4'! in such a position that the plates 45, 46 may swing about the axis of the cap screw 43 substantially without binding on the U-clip 42.

Swinging movement of the bracket 45, 46 about the axis of the cap screw 43 in a clockwise direction, as viewed in Fig. 2, is limited by an eye bolt 48. A pin'49 extending through the eye of bolt 48 is mounted in alined holes of the plates 45, 46 at a fixed distance from the axis of the screw 43, and the shank of the eye bolt extends through the brace 4I, oversize holes for the `shank of the eye bolt being formed in the top and bottom walls of the brace 4l, and the top wall being reinforced by an angle plate 59 which is welded to the brace 4I. A stop nut 5I and `a lock nut 52 are screwed upon the end of the eye bolt 4S which projects beyond the plate 55 at the upper sicle of the brace 4I, and the stop and lock nuts are drawn up tight against each other so that they will be retained in adjusted position longitudinally of the bolt 43. Engagement oi the stop nut 5I with the angle plate 5t limits swinging movement of the bracket 45, 43 about the axis of screw 43 in a clock wise direction, as viewed in Fig. 2, and the limit of said clockwise swinging movement of the bracket 45, 46 may be varied by adjustment of the nuts 5 I, 52 longitudinally of the bolt 48.

A swivel block 53, best shown in Fig. 4, is mounted on the bracket 45, 46 at a fixed distance from the axes of the cap screw 43 and pin 43, the swivel block 53 having oppositely extending trunnions journaled in alined holes of the plates 45 and 45. Cotter pins and washers on the trunnions at the outer sides of the plates 45, 43 keep the plates from spreading. The portion of the swivel block between the plates 45 and 45 has a smooth bore 54 which extends transversely of the trunnionaxis, the bore 54 aording a passage for a relatively long rod 55 which is supported within attempt the bore 54 for longitudinal 1 sliding -movementf' relative to the swivel blck in the direction Aofthel axis of the `bore 54; One end-ofthe rodf551tis. threaded 'to 'receive a2 castle nut 56; the threaded portion of the rod; inthe -position offthemecha,- nism'shown in -Figf. 2, extending beyond'fthe nut through the swivel block 53 and terminating. at

seme distance from the swivelblockat 'theside of the'latter remote-from the nut56i Theother4 end of the 'rod 55'has a relatively deepcounter bore 5l for` receptionfof a stem 582Which is slid=V ably `lit-ted into the counterbr'e 1 for back andi forth movement l'relative `totlie rodin the directionof its axis. The stemi58is -rigdly connected with a bifurcated headv59 which is pivotallyLconnected` with the hanger 32; an eye'fintegral with the hanger 32 lbeing straddledA by the prongs ofv the head 59. and a pin-5| extendingthrough the l prongs of the head '59 'and through the `eye 60.

A portion of the rod`55between`the swivel block 53 and the'head` 53is surrounded by a tube" 52 'whose inside diameter is slightly larger than theV outside diameter of the rod 55 Aso that the rodl 55 may slide in the directionof its axisrrelative to-the tube 62. The swivel-block 53 aordsa seat for oneendoiithe tube 62;r against which seat thetube is normally urged under consid# erable pressure-as will now bei described.

At the counterbored portion'of the rod 55 which `telescopical-ly engages the` stern 58,- acollar 53 is rigidly secured, asby welding, tothe rod 55. the collar being spaced some distan-cet from the end facel'oithe lrod'whiclr is abuttable by the head 59.? AsshowninFigs; 2 and 5, the collar 63fhasa central :hole through*whichthel rod 55 extends, anda circular boss `(idlis formed on the collar at the side'thereoffacingthe tube 52.' A iiange 55 extending radia-lli7A from thev boss 64 has flats 56 for the'purp'ose of holdingsthe rod 525 bymeans of ak wrench Vagainst rotation fwhen the nut `titi is -screwedlupenthe threaded end :of the rod during assembly andlwhen'an adjust-l ment is to be made by--turningofthe nut 56 Another collar 61 having a centralfcircular boss 68 `and a ilangefES-isrigidly securedasbyfweld ing, to the tube B2, the' collar 1611 being spacedv suitablel distance fromthe 'endoi the'tube 62 which abutsrthe `svvlvelblock 53,'A so as to'permit: swinging movement' et the rod 55 and tube 52' about the trunnion' axis ofthe swivel block 53T' without interference of the-collar "l-'with 4` the bracket 45, 45. Reacting between the collars 63' andlt` are two coilsprings; an outer` one HJ which is made of relatively heavy wire and which bears against the flanges E5 Aand'69," and lanirrv ner one 'il whichis made offsomewhat lighterwire and bears against thebosses 54 and 68T The bosses 54 |58l also servcft keep lthe outer coil spring lil centered relative to thefinner coil spring which turn is centered on the boss'iSS by the4 tube G2:

The distance between the. relatively opposed` faces ofthe ange's {i5-and 63 'as shownfinFig. Z'is substantially shorter than ythe-free length ofi the outer coil spring lil, the lengthAcf the threaded `portion of thev rod' 55 indicated vin ',Fig. 2 representingapproximately the-difference beev tween the free length of the coil springl and the spacing at which the relatively'opposed` faces of the flanges 65. and' aresho'wnin Fig. 2'.. Similarly, the distance between the" relatively opposed iacesof the bossesil and aa's shown in Fig. 2 is substantially shorter than theffree length .of the.Y innerfcoil:` spring 1|, the length Av ci f the.` threadedv portion l:ofl the: rod': 55..indicat.'

-tively;. The hanger 321is swingable-about the .2 4the spring numberrof Vturns ed s Figi 2;' again representing-i approximately' the'diierence between the free length of the innercoilfspring ll andthe spacing at which the relatively 'opposed faces of" the bosses 64` and fare'shown inFig.V 2; It will be seen that in the position of the mechanism-shown in Figf2 the Coil springs 710,1'1'!` are preloaded andthat the tube' 6`2isy urged against. the swivel block 53inoneadirection while the nut 56fis urged against'the swivel'blook 53 in the opposite directiofn'. ForI purposes of assembly the nut 56 maybe started on the threads of the rod 55 der` to i deflect thespring to the condition inv which it is shownin Fig. 2. However, the spring l'grasash'own, has.I a..relatively large number of turns "and'the ,coildiameter is likewise relatively large; soitha't'the spring TD will deflectat a relatively high rate inproportion to a deflectng load. Inuother wo1ds,'whi1e the spring l' is capable of exerting considerableV pressure; upon deflection'git 4has' a relatively large gradient of deflection, The inner spring 'H is made of somewhatrlighter wire than theouter spring l0, as; stated; `and its? coil diameter is Asubstantially srnallei",thanA the` coildiameter of vthe outer spri.c,l.:ll; The-numbery otturns ofthe inner spring is approximately the same-as that of the outer spring; and the size of the wire from which the inner spring is madegis suchthat deflection of therinn'er spring tothe preloaded condition inwhich'itis shown in Fig. 2 requires a relativelystrong. forcev comparable with the force which is required, as mentioned, to deflect the outerspring to its preloaded. condition. Like the outer spring, the` inner spring is capable of eX- erting considerable pressureupon deflection, and like the outer spring itv hasga4 relatively large gradient of deflection. Generally stated,lthe two coilsprings lil. 1I represent airelatively strong spring, unitwhich has a relatively large gradi.- entfoi deection,y andthe" rod 55, collars 63; 6l, and nut155= constitutefmeans for preloading said spring unit.y The rod. 55 `has va number of holes 12 inr tsthreaded" portion, and a cotter'pin 'i3 may he passed through any-of` these holes for locking the .castle nut :56 adjustmentalong-the; rod;55.

Afrelatively vweakooil spring '14, made of fi'lat wire 1 coiled r on edge, isf interposed between 'the collar l'53;andthe'head 59, the opposite ends of the spring. I4-,bearingagainstrelatively opposed faces of :the collar 63 and ofthe head 59, respec-v axis ofthespilvot 35 within arelativelywide range, as statede andfsaid range is such that the idler 3 could move from the'position in, which it is shown in'Figs. 1 and'Zto anappreciable extent in track tensioning-direction upon severance or removal of the track beltigf beforefthehanger 32 would reach its limit'of movement in said direction. In theposition of the parts asfshown in Figs. 1 and 'I4 is ina state of compression, and upon severanceor removal 'of 'the'track belt 5 the spring 'l4lwouldexpand toits free length and movef the'idler 3. in track tensioning direction from thaposition in which it is shown in Figs. 1 and'` 2;. Th'eewire size, 4thecoil diameter and the of thencoil. spring` 14 areY such iindiierent positions of that the expanding pressure exerted by the spring in its mentioned state of compression upon the collar 53 and the head 59 is substantially smaller than the thrust exerted by the preloaded coil springs l5, 1i against the collar 63 and which thrust is taken up on the swivel block 53 by the nut 55. For instance, the thrust exerted by the preloaded coil springs 1D, 'il may be twice as high as the expanding pressure exerted by the coil spring 'i4 in its mentioned state of compression. The coil spring it is further proportioned to have a relatively small gradient of deection as compared with the gradient of deflection of the spring unit lil, 'i i, that is, the coil spring 'Ml is so propor tioned that it will deflect at a relatively low rate in proportion to a deflecting load, and upon severance or removal of the track belt 6 the idler 3 would therefore be moved only a relatively small distance in track tensioning direction by the coil spring "M, On the other hand, a relatively short movement of the idler 3 in track releasing direction from the position in which it is shown in Figs. 1 and 2 would cause a substantial increase of the expanding pressure of the spring 'It due to its mentioned low gradient of deflection.

From the foregoing explanations, it will be seen ythat the resilient unit incorporating the coil springs 75, 'il and the resilient unit incorporating the coil spring 14 have diierent yielding charac teristics, the resilient unit incorporating the coil spring 'it being more readily deectable than the resilient unit incorporating the coil springs 1D, 1l.

Generally stated, the resilient unit incorporating the coil springs 1li, 1l represents iirst resilient means associated with the frame l in thrust transmitting relation thereto, and the resilient unit incorporating the coil spring lli represents other resilient means which are mounted for movement with the idler 3 and are arranged in tandem relation with the iirst resilient means.

Figs, l and 2 show the endless track mechanism in the condition which it assumes when the vehicle is at rest and the transmission chain 1 is relieved of driving power. In that condition the idler 3 occupies a normal track 'tensioning limit position, as shown in Figsfl and 2, and it will be noted that the end face of the rod 55 which is abuttable by the head 59, and the face of the head 59 opposite to said end face of the rod 55 are spaced from each other a certain distance indicated at B in Fig. 2. The strong expanding pressure of the spring unit l5, 'H is taken up at the swivel block 53, as stated, and the relatively light expanding pressure of the coil spring 'M urges the idler 3 in track tensioning direction and balances the pressure to which the idler 3 is subjected in track releasing direction due to the unsupported weight of the upper run of the track belt 6. It will thus be seen that the track belt is operative to determine the normal track tensioning limit position in which the idler 3 is shown in Figs. l and 2, and that in the condition of the mechanism as shown in said figures, the track belt 6 is maintained under an initial tension the extent of which is determined solely by the eX- panding pressure of the coil spring 'M It will further be noted that the rod 55 and the head 59 on the stem 58 represent stop means operable to limit deflection of the more readily deflectable resilient element 14. The rod 55 with its associated head 63, and the nut 56 on the rod 55 further provide tensioning means for the resilient elements represented by the coil spring 10, 1|, and said tensioning means are operative to preload the resilient elements 10, 1I independently preloaded spring unit ofthe resilient element represented by the coil spring 14 while the idler 3 is in its track tensioning limit position as shown in Figs. 1 and 2.

Assuming now that the vehicle is to be started under a relatively heavy drawbar load, and that propelling power is transmitted for that purpose through the transmission chain 'i to the sprocket 2 so as to rotate the sprocket in the direction of the arrow indicated in Fig. 1. In that case the track belt E becomes subject to a driving stress which is substantially higher than the initial tension of the track belt set up by the coil spring f4, and the spring 'i4 will therefore yield and the idler 3 will move from its normal track tensioning limit position in track releasing direction. The expanding pressure of the coil spring 1li which causes the initial track tension is substantially smaller, as stated, than the thrust exerted by the l0, 'H against the collar 53, and said thrust of the spring unit 10, 'Il is strong enough so that it will urge the nut 56 firmly against the swivel block 53 not only while the collar 63 is subject to the expanding pressure of the spring 'M which causes the initial track tension, but also while the pressure exerted by the spring l upon the collar 63 increases due to the mentioned track releasing movement ofthe idler 3. rIhe stem 58 will therefore slide within the counterbore 5'! of the rod 55, upon the mentioned track releasing movement of the idler 3 and the distance B will become smaller. However, the distance B, as indicated, is relatively short at the outset, and the head 59 will therefore engage the end face of the rod after a relatively Short movement of the idler in track releasing direction. Upon engagement of the head 59 with the end face of the rod 55 further movement of the idler 3 in track releasing direction would necessitate deflection of the preloaded spring unit T0, 'l l. The spring unit 1B, 1I, however, is preloaded to such an extent that it will not yield under the pressure which is exerted by the spring I4 upon the collar B3 and by the head 59 upon the rod 55 when the track belt 6 is subjected to the driving stress which is necessary for developing the full drawbar pull of the vehicle. Accordingly, when the vehicle is started to pull a heavy load the head 59 rst moves into engagement with the end face of the rod 55, and after a correspondingly short movement of the idler 3 in track releasing direction from the position in which it is shown in Figs, 1 and 2, driving stress is permitted to build up in the track belt against the action of the preloaded spring unit lil, Il until the vehicle starts to move. The function is the same when the vehicle is started abruptly under a relatively light load or whenever the drawbar load is such as to require a sufficiently high driving stress in the track belt to force the head 59 against the end face of the rod 55.

Movement of the idler 3 from the position in which it is shown in Figs. 1 and 2 to the position in which the head 59 engages the end face of the rod 55 causes a shortening of the center distance between the sprocket 2 and the idler 3, and the lower run of the track belt will therefore slacken. The distance B in Fig. 2 is short enough to keep said slack of the track belt at a proper limit so as to avoid derailment of the truck rollers. The upper run of the track belt is held taut regardless of the shortening of the center distance because it is under driving stress. During starting and while pulling a heavy load the driving stress in the upper run of the track belt is relatively high, as stated, and while the upper run is under said .ismoving slowly, the upp engagement with the .of the idler the rodf55 v impede the packing `eration of the mechanis high driving stressiand as longfras thevehcle erruni of` the track belt will have no tendency to whip up and down. However, when the vehicle is driven ata relatively high speed, say between 30 'and 40 miles per hour, centrifugal and other forces acting upon the track belt tend to induce `whipping of theupper run `of the track belt. Due to the provision of the coil spring 'I4 such up and down whipping of the upper run of the track belt under theinentioned conditionsis suppressedbefore it reaches an undesirable or objectional amplitude. T-he spring 'I4 has a relativelyvlow. gradient of deilection, as stated, with the result that its expandingpressure varies materially upon relatively short deflections of the spring, and the, effect of the spring'IlI is to dampen vertical oscillations of the upper run of the track belt.

While the vehicle is o conditions cause the i perated, changing driving dier 3 to moveback` and forth against the action of` the coil springgl more or less continuously. .The driving stressin the upper run of thetrack'belt may at times .be high enough to force the head 59 against' the end face ofthe rod55, and at other,timesfor Yinstance when coasting, vthe head Vlill may be forced out of endiace ofthe rod 55 by re of the coil spring "I4, back and forth movement may become subject to imore or less violently. `These tics of the mechanism are beneficial effect because they of .mud and the'formation of an ice crust around the hanger 32 andaround nd 14, which would inhibit opm or prevent it yfrom working when a stone or like obstruction becomes lodged between the track belt .and one of the wheels. Similarly, the pivot joints at 35 and 6I and the sliding joint of the counterboredend of the rod 55 with the stem 58 are not liable to become stuck, as by rust.

Assuming that a stone on the lowerrun of the track belt is drawn into engagementwith the idler 3 and is forced to pass with the track belt around the idler 3. In that case the head 459 will be urged into engagement with the end face of the rod 55, if it is not already so engaged, and the track tension rises to the'point where the preloaded spring unit 10, 'II begins to yield. The spring unit '10, 'II, as statedhas` a relativelylarge gradient of deflection, and itwilltherefore yield to the necessary extent for letting the stone pass around the idler, while pressure of the spring unitll), 'II r atively small amount beyond t which it is preloaded under no It will be noted that the ha rod 55 form two links ofa t through which the preloaded is deflected when the idler 3 releasing direction beyond th the head 59 engagesthe end Designating the hanger 32 a toggle mechanism, and therod55 has a second link, it will be noted that the rst link 32 is pivotally mounted on the frame Il at 35, and that the second link 55 is mounted on the frame I for pivotal and translatory movement relative. thereto, the rod 55 `being pivotallymovable together with the swivel block 53 relative to the frame I about the trunnion axis of the swivel block 53, and translatory movement of the rodw55relative to the frame I" being afforded'by the slidable the expanding pressu During the mentioned pact by the head 59v m operating characteris desirable and have a the springs 'IIJ, II a ises only a relhe pressure to rmal conditions. nger 32 and the oggle mechanism spring unit 10, 'II is forced intrack e point at which face of the rod 55.

' 25 i unfit 145 fimakefaireediuSt-m-rlt the expanding @'15 sito` reiativei amounting of tithe rod #.255 in :the bore' :swivel block before Y I'It `will flurtherfbevn 5 betweenithefirstilinkl Lby means cfithelstem: 5&3 .provides for :pivotal .'54 0f the 253, as has @been explained `hereinoted :that :the @connection 32 andthe;.secondlinkz55 .58, vand. its: associated: head `and translatoryymovement ofi tlieisecond;l Jinkf55`srelativeyto .ther firstilink 1'32'. As Ther stem eiland -itszzassociatedrhead ,59 .con- 10. .istituteri in' aeiect, La athird linkt-ofi the :mentioned toggle-.nrechanism;` and .saidtthird link; ispivotally connected with the first link 32i=atif6lgandzhasia .wsliding connection;.at 5Iiwiththe secondizlink 55. line i through thc t axis. of. the joint 35" and thnoughithe. tr-.unnion' axis; of the;` swivel block` 53 :represents thesdead vcenter lineof the mentioned -,toggle mechanism, and \when the spring l'Ill .r/yields. the; pivot4 pin 26 I moves; towards, said; dead center` line, and upon subsequent, yieldingI move- Zolfment of the, spring unit J0, 1I .thegpivotopin` 6I ,continues `to approachlsaid-.dead center line. ,The hanger 32,;land rod 1:55, f therefore, @have a iforce multiplying ,effect upon the spring unit 10,v v1. l apdffwhile' the rexpandingtpressure 4of` thespring 0,; 'I Iri-ses `at a relatively'` lowrate, :as stated, ,uponideilection of said ,spring gunit, tha-eiective xforce uponthe ,hanger 32 which restrainsithe idler ,3 1 fromgmovngfbe ,ond Q the point at .which t thehcad 59- engagesthe endface;,of.the-.rod,;55, rises ata: still lower rate.

Operation of the vehicle will cause a cer-tain 4wear. of, the Vfaces ofj the .rail beltsQ kand i0- which .cooperate i with. the Ltruck:rollers 4I and with,v the leeine i Permanently .elensated to f some extent, as by permanent elongation, of vvthecables lf2 and 40,- I3 i under a the y .driving stresses. :Such wear ;and

elongation willy beA compensated@ for automatically, by the coil spring 14, atileast to, the j extent A,or makingY.frequentreadustmentsf of lthe mech- Aanisrn unnecessary. If `the .mentioned causes necessary `this, can be actly V by readjustrnent Lof :the ently, of or in conjunction of-the nut 56.` :Adjustment independently of thernut 56 Acornplished convenien v.nuts Af5 I, 52, independ with a readjiistment of the-nuisent:

affects [only the .distance f B. in .-Eig 2, and lad- Ljustment off-thenute'j independentlyof the .nuts ,5 I l:'52 .affects :the i preloading `of the coil `springs K 'IlLv .1 I and also the t distance f B. L Obviously,` the `springs `"III, 'II and," canbe adjusted toy exert 5 theirv` desired `pressures )oy-adjustment of, the nuts l5I,f52 and 56. v1 l'1 e pressure\condition of v, the springf'lL-and, t ereforefthe,initialetension of the `tra-ck f belt can 1 be conveniently checked by Ameasuring the clistance,C;in;Fig. 2 betweenfthe y yfopposedfaces of thecollarffandbf thehead;53.

While inthe foregoing .a. preferred embodiment .oftheinventionihaswbeen disclosed., it should be rwunderstoodthat:it is notintended to ylimitthe i 4invention tothe exact design :and ,detai-Isof constructiomherein described vand shown forivarilVousYmodilcations within :the scopepof thevappended claims maymoccurtoipersons `skilledwin the art. 7o I tly-is, claimed-an (Patent:

4,1. 1n auself-layin d, desiredto secure by :Letters g `track Tmechanism -of the 7typein.,. wh ich as tructurel'for operatively mount- 5 ing Ian,endless ,tracks belt. comprises a frame and a v.track engaging @wheel mounted .onf ,s ad frame for movement relative thereto in track tensioning and track releasing directions, and in which said track belt is operative to determine a normal track tensioning limit position of said wheel, the combination of first resilient means associated in thrust transmitting relation with said frame, second resilient means having a yielding characterteristic different from that of said rst resilient means, and means mounting said second resilient means for movement with said wheel relative to said frame and in tandem relation with said iirst resilient means.

2. In a self-laying track mechanism of the type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging Wheel mounted o-n said frame for movement relative thereto in track tensioning and track releasing directions, and in which said track belt is operative to determine a normal track tensioning limit position of said Wheel, the combination of first resilient means associated in thrust transmitting relation with said frame, second resilient means mounted for movement with said wheel relative to said frame and arranged in tandem relation with said iirst resilient means, one of said resilient means being deflectable more readily than the other, and stop means operable to limit deflection of said more readily deflectable resilient means upon movement of said wheel from said limit position in track releasing direction.

3. In a self-laying track mechanism of the type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, and in which said l track belt is operative to determine a normal `track tensioning limit position of said wheel, the

combination of first resilient means associated in thrust transmitting relation with said frame, second resilient means mounted for movement with said Wheel relative to said frame and arranged in tandem relation With said iirst resilient means, and tensioning means for vone of said resilientmeans effective to preload said one resilient means independently of the other While said wheel is in said limit position.

4. In a self-laying track mechanism of the type in which a structure for operatively mounting an endless track belt comprising a frame and "a track engaging Wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, and in which said track belt is operative to determine a normal track tensioning limit position of said Wheel, the combination of rst resilient means associated in thrust transmitting relation with said frame, second resilient means mounted for movement with said Wheel relative to said frame and arranged in tandem relation with said first resilient means, tensioning means for one of said resilient means effective to preload said one resilient means independently of the other while said Wheel is in said limit position, and stop means operable to limit deflection of said other resilient means upon movement of said Wheel from said limit position in track releasing direction.

5. In a self-laying track mechanism of the'type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging wheel mounted on said frame for movement relative thereto in track tensioning and track' releasing directions, and in which said vtrack belt is operative to determine a normal v tensioning track tensioning limit position of said wheel, the combination of a first resilient element associated in thrust transmitting relation with said frame, a second resilient element deectable more readily than said iirst resilient element, and means mounting said second resilient element for movement with said Wheel relative to said frame and in tandem relation with said first resilient element.

6. In a self-laying track mechanism of the type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging Wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, and in which said track belt is operative to determine a normal track limit position of said Wheel, the combination of a iirst resilient element associated in thrust transmitting relation with said frame, a second resilient element deflectable more readily than said first resilient element, means mounting said second resilient element for movement with said Wheel relative to said frame and in tandem relation with said rst resilient element, and relatively movable stop means associated, respectively, with said first resilient element and with said wheel and movable into cooperative engagement with each other to limit deection of said second resilient means upon movement of said Wheel from said limit position in track releasing direction.

7. In a self-laying track mechanism oi the type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, the combination of a first resilient element, means mounting said rst resilient element in initially deflected condition on said frame and independently of said Wheel, a second resilient element deflectable more readily than said initially deflected rst resilient element, and means mounting said second resilient element for movement with said wheel relative to said frame and in tandem relation With said initially deflected iirst resilient element.

8. In a self-laying track mechanism of the type in which a structure for operativeiy mounting an endless track belt comprises a frame and a track engaging wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, the Icombination of a rst resilient element, means mounting said rst resilient element in initially deected condition on said frame and independently of said Wheel, a second resilient element deectable more readily than said initially deflected rst resilient element, means mounting said second resilient element for movement with said wheel relative to said frame and in tandem relation with said initially deflected first resilient element, and relatively movable stop means associated, respec- 13 wheel and pivoted on said frame, a second link member mounted on said frame for pivotal and translatory movement relative thereto, means connecting said second link member with said i'irst link member for pivotal and translatory movement of said second link member relative to said rst link member, and rst and second resilient elements mounted to react, respectively, between said frame and said second link member, and between said rst and second link members, and eiective to yieldingly oppose movement of said wheel relative to said frame in track releasing direction.

10. In a self-laying track mechanism of the type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, the combination of a rst link member rotatably mounting said Wheel and pivoted on said frame, a second link member mounted on said frame for pivotal and translatory movement relative thereto, a third link member pivoted on said rst link member and slidably connected with said second link member, and iirst and second resilient elements having different yielding characteristics and mounted to react, respectively, between said frame and said second link member, and between said second and third link members, and effective to yieldingly oppose movement of said wheel relative to said frame in track releasing direction.

11. In a self-laying track mechanism of the type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging Wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, the combination of a link member rotatably mounting said wheel and pivoted on said frame, a bracket mounted on said frame for pivotal movement relative thereto independently of said link member, means associated with said bracket and cooperable with said frame for pivotally adjusting said bracket relative to said frame, and tandem connected iirst and second resilient means having different yielding characteristics, operatively interposed between said bracket and said link member and effective to yieldingly oppose movement of said wheel relative to said frame in track releasing direction.

12. In a self-laying track mechanism of the type in which a structure for operatively mounting an endless track belt comprises a frame and a track engaging Wheel mounted on said frame for movement relative thereto in track tensioning and track releasing directions, the combination of a iirst link member rotatably mounting said wheel and pivoted on said frame, a bracket mounted on said frame for pivotal movement relative thereto independently of said iirst link member, means for pivotally adjusting said bracket relative to said frame, a second link member mounted on said bracket for pivotal and sliding movement relative thereto, a third link member pivoted on said first link member and slidably connected with said second link member, and rst and second resilient means operatively interposed, respectively, between said bracket and said second link member and between said second and third link members, and eiective to yieldingly oppose movement of said wheel relative to said frame in track releasing direction.

IGOR A. KAMLOOKI-IINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,368,652 Pennington et al. Feb. 15, 1921 1,981,867 Knox et al Nov. 27, 1934 2,315,421 Heaslet Mar. 30, 1943 

